Method of removing oil from water



Aug. 25, 1964 J. w. FELLA METHOD OF REMOVING OIL FROM WATER United States Patent O 3,146,185 METHOD OF REMOVING OIL FROM WATER James W. Fella, Baytown, Tex., assigner to Standard Oil Company, Chicago, Ill., a corporation of Indiana Filed May 22, 1961, Ser. No. 111,751 3 Claims. (Cl. 208-48) This invention relates to a method of removing soluble and entrained insoluble oil from oil-laden water obtained during a delayed coking operation and in particu-Y lar it relates to a method which permits the use of the oil-laden water in the hydraulic decoking cycle of the coking operation. In addition, it relates to a method of reducing the oil content of waste water to a level which permits the water to be easily disposed of in the refinery efiiuent water.

Oil-laden waste water presents a real problem in the disposal of waste water froml a refinery which is either located on inland waters where such waters are used for drinking purposes or located on inland bays or river outlets where oysters and other fish foods are grown for commercial purposes and thus are protected by fish and game laws. In addition, at a number of refineries the lack of adequate fresh water supply has become a prob# lem. As industries continue to use increasing amounts of fresh water, all means of conserving the fresh water by reemploying usable contaminated water in refinery operations must be observed. Heretofore, the delayed coking operation has Iresulted in a substantial amount of oil-laden waste water which cannot be reused and must be disposed of with the refinery efiiuent Waste water. The water used in the hydraulic decoking cycle of the coking operation must have a very low oil content since any significant amount of oil will cause emulsion of the high pressure centrifugal pumps used for pumping the Water under pressure to the jets during the hydraulic decoking. The emulsion substantially reduces the effectiveness of hydraulic decoking. Heretofore water used in the delayed coking operation has been disposed of after becoming oil-laden. This necessitates additional treating facilities and the use of substantial amounts of fresh water makeup. It is therefore an object of this invention to provide a novel method for removing oil from oil-laden waste water obtained from la delayed coking operation, which method permits the reuse of the Water in the coking operation and materially reduces the waste Water disposal problem.

In the operation of coking crude oil and, more particularly, a process of delayed coking, a reduced crude feed stock is rapidly heated in a flowing stream by way of a pipe still. The heated stream from the pipe still is charged to a coking drum. The feed stock in the coking drum deposits a residual coke material in the drum and gasoline and gas-oil are Withdrawn from the drum and passed to a fractionator. It is the usual practice to recycle a portion of the gas-oil product from the fractionator and contact the coke drum vapors with this reduced crude feed. The delayed coking process is, therefore, a combination of a distillation process and a thermal cracking process. When a coking drum becomes filled with coke, the general practice is to divert the feed stream of hot hydrocarbons to an adjoining empty coking drum which is preferably preheated. Coke is then removed from the first drum. The process of removing the coke from the first drum requires that the drum be cooled and the coke removed by mechanical or hydraulic means.

In practice, the water used for hydraulic decoking is kept separate from the water used for cooling the coke bed subsequent to the coking cycle, since the water used for hydraulic decoking must contain no oil or only a very small amount to avoid emulsion problems. Nor- 3,146,185 Patented Aug. 2K5, v19621` ice mally it is the practice to use fresh Water as the makeup' water for the hydraulic decoking` step. After the cokebed has been formedY in the coke drum during the cokingoperation, the temperaturev is about 900 F. and must be lowered to less than 212 F. in order that the hydraulic decoking cycle may proceed. Water introduced into the hot coke bed is vaporized along with oil vapors and withdrawn from the coking drum to-a blowdown drum. The'water is continued to be introduced until the `bed temperature is less than 212 F., at which time the interstices are filled with water. The water in the coke drum is then withdrawn to a clear water tank. The water andk oil vapors which have been taken overhead to the blowdown drum are condensed and passed to a settling pond where oil is permitted to rise to the surface and is skimmed off. Even with a reasonable size skimming pond and a reasonable amount of settling time, there remains in the condensed water soluble and entrained insoluble oil to the extent that it cannot be used for the hydraulic decoking cycle without causing emulsion in the high pressure centrifugal pumps and subsequent emulsion in the coke bed during the cutting. It has been the practice heretofore to discharge this water to an API separator for rejection with the refinery Waste water effluent. Thus the separator is either overloaded or additional treating costs are incurred in order to reduce the oil concentration in the water to a level within thelimits permitted by law for discharge' to a body of water used for drinking purposes or controlled for growth of oysters, clams and other fish foods. In addition, the use of fresh water makeup for the coke cooling cycle increases the consumption of fresh water. v

I have discovered a method whereby substantial savings of fresh water makeup can be obtained in the delayed coking operation by a technique that removes the oil from oil-laden water which was formerly discharged from the operation. This technique is to use the oilladen water as cooling Water during the hot coke bed cooling cycle. When the oil-laden water is Withdrawn from the hot coke bed, the water contains less than ppm. of oil. At this oil concentration the water is suitable for use in the hydraulic decoking cycle without causing emulsion.

My invention will be better understood by reference to the annexed drawing and the following description. The drawing shows a partial view of the delayed coking unit. Means for heating and introducing the oil to the coking drum and means for carrying out the coking cycle are not shown. Neither are means shown for hydraulic decoking of the coke drum and the removal of the discharged coke. After coking drum 11 has been filled with coke during the coking cycle of the delayed coking operation, the temperature of the bed is about 900 F. and must be cooled to below 212 F. before the hydraulic decoking operation can proceed. The cooling of the hot coke bed is effected by introducing water from tank 12 through lines 13 and 14 and valve 15 by pump 16. The water entering coke drum 11 is vaporized by the hot coke and Water vapors laden with oil are Withdrawn through line 17 and passed to blow down drum 18 where the oil and water vapors are condensed. The introduction of water into the hot coke bed is continued until the temperature of the coke in coke drum 11 is less than 212 F., at which time the interstices in the coke drum are filled with Water. After this the water is withdrawn through line 19 and valve 20 to tank 12 where it can be reused for coke bed cooling or during the hydraulic decoking cycle. The condensed water and oil vapors in blowdown drum 18 are passed by line 20a to the first stage of skimming pond 21 where the bulkgof the oil is removed from the surface by skimmer 22. The oil then passes into the second stage of the skimming pond 21 where further oil is removed by skimmer 23. Even after more than a reasonable amount of settling and skimming, the skimmed water from the second stage of the skimming pond contains up to about 2000 p.p.m. of oil. Since water containing this amount of oil will emulsify in high pressure centrifugal pumps and in the coke bed during the hydraulic decoking, heretofore this water has not been used further in the coking process. Consequent- 1y, the Water separated in the second stage of the skimming pond was passed to the API separator for further processing before discharge to the renery waste water eluent. Substantial amounts of water were introduced and discharged during a complete cycle of the delayed coking operation. By practice of my invention I have found that if the oil-laden water from the second stage of skimming pond 21 is passed by line 24 to the suction side of pump 16 and introduced to coking drum 11 during the hot coke cooling cycle, the water withdrawn from the cooled coke in coking drum 11 to tank 12 contains less than 100 p.p.m. of oil. Thus the oil-laden water which has heretofore been discharged from the delayed coking unit is freed of the bulk of the soluble and entrained insoluble oil and conserved for further use in the delayed coking operation. Any emulsion that may be formed when using the oil-laden water in the cooling step will not interfere with the cooling of the bed and will be broken when brought into contact with the hot coke.

It can be seen that by the practice of my invention a unique method of removing oil from Water is achieved. Contrary to a filtering step wherein a bed of absorbent material would have to be activated and discarded or regenerated after saturation, the oil removed from the water by the hot coke during the cooling cycle adheres to the coke and is removed along with the coke during the decoking cycle of the coking operation. In eiect, with each new bed of hot coke a new water-treating bed is available. Contrary to what was expected, the quality of the coke obtained from the coking unit was not altered by the practice of my invention.

In the operation of a renery on an East Coast inland bay which contains oysters, clams and fishes protected by sh and game laws, it has been necessary to use elaborate means to assure that the waste water being discharged to the bay is of sufficiently low oil content so as not to impart odor or taste to the sh. As the refinery expanded, means for conserving fresh water supply and reducing the load on the waste water cleanup plant were also needed. The practice of my invention resulted in a solution to this problem. Skimmed water separated from the second stage of the skimming pond contained about 1600 p.p.m. of oil. This water was introduced into a hot coke bed of a delayed coking unit during a cooling step and used to cool a bed of coke about feet high. The water which was withdrawn from the cooled bed of coke contained less than p.p.m. of oil and was suitable for use in a subsequent cooling cycle or for a hydraulic decoking cycle.

It will be understood that numerous modifications and variations in the system outlined above can be carried out without departing from the spirit of this invention, which is set forth in the appended claims.

I claim:

1. The process of removing soluble and entrained insoluble oil from an oil-laden water to be used in the hydraulic decoking of a coke bed contained in a coking zone of a delayed coking unit which method comprises introducing the oil-laden water into a hot bed of coke in the coking zone during the coke cooling cycle of the delayed coking operation, removing oil-laden water vapors from the said coking zone, continuing to introduce the oil-laden water into said coke bed until the coke bed is cooled and interstices within the coking zone are lled with water, withdrawing a clarified water from the bottom of the coke bed and subsequently using said withdrawn water in the hydraulic decoking cycle of the delayed coking operation.

2. The process of claim 1 wherein the oil-laden water contains not more than about 2000 parts per million of said oil and the coke bed is cooled to below 212 F. during the cooling cycle.

3. The process of claim 1 wherein the water withdrawn from the cooled coke bed contains not more than about 100 parts per million of oil.

Sperr Sept. 18, 1934 McMahon Mar. 29, 1960 

1. THE PROCESS OF REMOVING SOLUBLE AND ENTRAINED INSOLUBLE OIL FROM AN OIL-LADEN WATER TO BE USED IN THE HYDRAULIC DECOKIING OF A COKE BED CONTAINED IN A COOKING ZONE OF A DELAYED COKING UNIT WHICH METHOD COMPRISES INTRODUCING THE OIL-LADEN WATER INTO A HOT BED OF COKE IN THE COKING ZONE DURING THE COKE COOLING CYCLE OF THE DELAYED COKING OPERATION, REMOVING OIL-LADEN WATER VAPORS FROM THE SAID COKING ZONE, CONTINUING TO INTRODUCE THE OIL-LADEN WATER INTO SAID COKE BED UNTIL THE COKE BED IS COOLED AND INTERSTICES WITHIN THE COKING ZONE ARE FILLED WITH WATER, WITHDRAWING A CLARIFIED WATER FROM THE BOTTOM OF THE COKE BED AND SUBSEQUENTLY USING SAID WITHDRAWN WATER IN THE HYDRAULIC DECOKING CYCLE OF THE DELAYED COKING OPERATION. 